Polyester resins, represented by polyethylene terephthalate (“PET”), possess excellent mechanical properties and chemical properties, e.g., excellent transparency, gas barrier properties, safety and sanitation and the like. As such, they have been used widely particularly in the food packaging field, as bottles obtained by stretch blow molding of an injection-molded preform, as trays or cups obtained by thermoforming of an extrusion-molded sheet, or as films obtained by biaxial stretching of the sheet.
PET can be made by condensing ethylene glycol and terephthalic acid. To increase its gas barrier properties, resorcinol di(oxyacetic) acid (RDOA) or 1,3-phenylene dioxydiacetic acid has been used as a co-monomer in the polymerization process. The use of the RDOA monomer was found to be effective in enhancing the barrier properties of polyesters, polyamides and their copolymers.
RDOA can be synthesized from resorcinol from two different routes. In the first method, resorcinol is first converted into bis(hydroxyethyl)ether of resorcinol, which is subsequently oxidized to produce RDOA. In the second method, RDOA can be obtained directly from the reaction of resorcinol with chloroacetic acid under alkaline conditions. Of these two methods, the chloroacetic acid route could be more economical and straight forward, but the yield of RDOA obtained from the chloroacetic acid route has been often relatively low due to the formation of various by-products.
Therefore, there is a need for a process to make 1,3-phenylene dioxydiacetic acid (i.e., RDOA) and its analogs in a relatively higher yield. Preferably, the process also produces relatively higher purity products.